Life looks better in colour. Vivacious reds, deep sultry blues and bright invigorating yellows all serve to lighten the soul. We perceive these colours from human eyes picking up a huge range of light frequencies, and we are limited by the frequencies we can pick up. This limitation is referred to as our visible spectrum, and ranges from primary red to deep violet and encompassing all the blues, greens and yellows in between. This spread of colour is known as the “colour gamut” of vision.
While nature has given us quite a wide range of colours to see, the devices we use to produce colours and images have an even more restrictive gamut. The two that have the most impact for photographers are printers and monitors. These two groups of devices use very different ways of making colour namely additive and subtractive colour. Understanding these, and the effect they have on your final images, can change the quality of print you end up with significantly.
for more go to Source: How Colour Works - Digital Photography School